Operating within the hydrate formation zone using low-dosage hydrate inhibitors (LDHI) is an emerging technical solution that may allow reducing capital investment and operating costs. Risks and efficacy of these additives is commonly assessed prior to field application; however, this process rarely considers a key multiphase flow characteristic – the flow pattern of the system. Incorporating this key variable would improve the confidence in the performance of LDHI for gas dominated systems and allow safer operations.
The Additive and Hydrate at the Top of Line (AHToL) joint industry project acquired knowledge and data for gas dominant conditions using the 140 m long and two inch (5.08 * 10-2 m) Lyre loop pilot. The hydrate formation tests were performed under multiphase flow conditions to assess the transportability and identify risks such as hydrate plug formation and hydrate formation at the top of line with and without LDHI.
Two commercially available anti-agglomerant additives (AA-1 and AA-2) were tested in gas / condensate / water system at two water cuts under different multiphase flow regimes. The tests were analysed based on pressure, temperature and pressure drop measurements along the loop, visual observations at a given position and monitoring of the overall free gas compositions and consumption.
Firstly, a comparison of the two AA additive performances is presented under stratified flow. The two additives showed different behaviours regarding hydrate formation kinetics (exothermic peak locations, induction time, hydrate structure, conversion rate, …), hydrate distributions (either in the flowing liquid or adhering at the top of the line), and pressure drop evolutions.